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A mononuclear complex with long alkyl chains, [FeII(H2Bpz2)2(C9bpy)] (1; H2Bpz2 = dihydrobis(1-pyrazolyl)borate, C9bpy = 4,4′-dinonyl-2,2′-bipyridine), was synthesized. Single-crystal X-ray crystallographic studies revealed that the Δ- and Λ-forms of the complex co-crystallized in the lattice asymmetric unit, while magnetic measurements unveiled that this complex underwent incomplete one-step spin crossover (SCO) with the transition completeness and temperature depending on the measurement velocity because of slow spin equilibrium. Multivariable approaches such as varying scan rate, annealing the sample, light irradiation and pressure have been adopted to effectively overcome the slow spin equilibrium and thus improve the SCO completeness. [ABSTRACT FROM AUTHOR]

Hofmann-type spin-crossover (SCO) frameworks attract much attention due to their predictable structures and diverse SCO behaviours. In this paper, we report two isostructural two-dimensional (2D) Hofmann-type SCO frameworks [FeII(ppe)2MII(CN)4]·3H2O (ppe = 1-(2-pyridyl)-2-(4-pyridyl)ethylene and M = Pd for 1 and Pt for 2). X-ray crystallographic studies, magnetic measurements and Mössbauer spectra jointly reveal that both compounds undergo complete hysteretic two-step SCO, i.e. HS1.0 HS0.6–0.5LS0.4–0.5 LS1.0 conversion with thermal hysteresis loops of 14 K and 28 K wide for 1 and 13 K and 26 K wide for 2. The dehydrated samples, 1-dehydrated and 2-dehydrated, display different SCO behaviours, unveiling that the SCO behaviours are affected by guest water molecules. [ABSTRACT FROM AUTHOR]

Three one-dimensional looped coordination polymers with the formula of [Fe(dpds)2{C(CN)3}2]·dpds (1, dpds = 4,4′-dipyridyl disulfide), [Fe(dpds)2(NCBH3)2] (2) and [Fe(dpds)2(NCSe)2]·3.5H2O (3) have been synthesized and characterized by single-crystal X-ray crystallography, Mössbauer spectroscopy and magnetic measurements. The spin-crossover (SCO) behaviors of these compounds depend significantly on axial ligands: compound 1 exhibited thermal-induced complete one-step SCO behavior with a T1/2 of 170 K, and 2 showed incomplete SCO behavior with T1/2 being 130 K, whereas 3 was paramagnetic. Meanwhile, both compounds 1 and 2 displayed light-induced excited spin-state trapping (LIESST) effects, featuring TLIESST values of 45 K and 61 K for 1 and 2, respectively, which were independent of exciting laser wavelengths. These results suggest that anions such as C(CN)3− and NCBH3− with much stronger ligand fields are needed in order to realize spin-state switching, if a ligand such as dpds is adopted to synthesize SCO compounds. [ABSTRACT FROM AUTHOR]